The present invention relates to the general field of moving blades for turbomachines such as the blades for the fan of a turbomachine.
The fan blades of a turbomachine are subjected to speeds of rotation that can impart subsonic to supersonic speeds to the gas flow passing through the fan. Although high flow speeds make it possible in particular to improve the flow rate of the gas so as to increase the thrust of the turbomachine, they nevertheless present the drawback of generating a large amount of noise. In particular, the “supersonic shockwave” corresponding to the changeover from supersonic speeds to subsonic speeds in the gas flow contributes a major fraction of this noise. Other interaction phenomena involving the turbulence of the gas flow in the proximity of the fan (broadband noise) also constitute sources of noise.
Engine manufacturers therefore seek to design fan blades that enable thrust to be increased, while minimizing the noise generated by the gas flow. In addition, when designing such blades, various other parameters need to be taken into account such as aerodynamic and mechanical considerations involving the blades. The blades need to be designed so as to optimize the flow rate and the compression of the gas flow passing through the fan while guaranteeing that the blades present good mechanical strength. In particular, at high speeds of rotation, the mechanical stresses to which the blades are subjected are very severe because of the high levels of vibration and because of the centrifugal force that is applied to the blades.
Numerous fan blade shapes have been proposed. They are characterized mainly by their relationships for stacking blade sections, by their general curvature, and by the optional presence of a swept shape for the purpose of improving aerodynamic performance and reducing the noise generated by the fan. Nevertheless, none of those blades makes it possible to obtain aerodynamic operation that is effective under all conditions of use of the turbomachine, in particular at full power (e.g. during takeoff and at the end of the airplane climbing) and at partial power (e.g. during the approach stage of the airplane), while complying with noise standards that are becoming more and more strict.